1. xguard

    xguard Member

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    I've read you can fit 275/60/15s on a 72 Demon if you nail the back spacing. Looks like I missed it. 15x8s with 4.5 back space. That seemed to be the magic formula. But my car is small bolt pattern with the standard 10 inch drums. Maybe that's the difference. Thoughts? Options? Really limited on wheel options for small bolt pattern. (Btw the back of the car is sitting a little higher because of the weight distribution on Jack stands.) Will probably throw some 255s on the old wheels until I can upgrade to big bolt pattern.

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  2. Slantsix64

    Slantsix64 Well-Known Member

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    4.25 bs with the small bolt would of worked, but just use a spacer 1/4 you got long studs already, but you would need to roll the fender lip a bit nothing to crazy, thats if you need too.
     
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    • 71GSSDemon

      71GSSDemon Well-Known Member

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      • George Jets

        George Jets 1967 Dart 2 Door FABO Gold Member

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        255s are a nice size tire, here they are on the back of a B.

        20200803_230827.jpg
         
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        • duster2

          duster2 Well-Known Member

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          Here is the thing , they say the backspace is 4 , 4.25 or 4.5 , but is it actually that. I have bought wheels from Jegs and Summit , because Specialty Wheel didn't offer 4.25.
          I tried 4.5 , hit the spring with 275's , actual backspace was 4 5/8 and 4 11/16. So I ordered a 4 inch backspace , got 4 1/4 and 4 3/8. Swapped wheels side to side to see what worked best. My Duster has a good 1/8 to 1/4 difference , side to side. Sure would be nice if they followed their own specs.

          Frank
           
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          • zakimodo

            zakimodo Well-Known Member

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            Something that bit me was not factoring the tires actual section width when I did my measurements. If the tire was no wider than the tread width it probably would have tucked in there fairly well.
             
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            • 71GSSDemon

              71GSSDemon Well-Known Member

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              This is why I went with a 15x8 instead of the 15x7 also. I figured the wider rim would lessen the "sidewall bulge" that the 7" would have.
               
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              • xguard

                xguard Member

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                How do they fit on the quarter panel side?
                 
              • pishta

                pishta I know I'm right....

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                That's opposite what the tire will do in my opinion. larger base will extend the bead width but the cross section is fixed. Going to a more narrow rim may change that sidewall to a more narrow overall width (just because it has to reach back for the rim bead) but that is not recommended as the tire is designed for a specific size bead width. space your rim out 1/4 and roll that fenderlip with the lip roller that swings in an arc off the hub after carefully starting the trim flange to bend up. Looks like you have plenty more room if that lip is cleared, like most A-bodies.
                 
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                • 71GSSDemon

                  71GSSDemon Well-Known Member

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                  I have no issues or concerns at all with the tire fitment. The car is unmodified in the wheel wells, no spacers, and survivor with 23,090 miles.

                  Tire Fitment 1.jpg

                  Tire Fitment 2.jpg
                   
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                  • xguard

                    xguard Member

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                    That looks great to me. Is the back end sitting a little higher than stock? Air shocks or different leaf springs?
                     
                  • TF360

                    TF360 Well-Known Member

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                    4 1/4 backspace with 255's - Don't go bigger unless you want to problems
                     
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                    • 33IMP

                      33IMP Well-Known Member

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                      I couldn't agree with slantsix64 more. I love wheels with too much backspace, that can be fixed/adjusted with spacers. Too little, the tire crashes into the fender. As he pointed out, you already have the necessary studs. No brainer in my opinion!
                      Next, I think the reason that it didn't work, going in, is cause of the narrow brakes on a sbp 8 3/4, the wheel mounting face-spring distance is a little shorter than the average
                      8 3/4.
                       
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                      • sireland67

                        sireland67 FABO Gold Member FABO Gold Member

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                        This is my car 275/60/15 on a factory 15 x 7 with 4.25" back space, plenty of room between the springs and 1/4 panel. No spacers.

                        Ny87vQ.jpg
                         
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                        • TF360

                          TF360 Well-Known Member

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                          Sireland, I cant believe how much space you have on the outside- You don't get that on a 74 Duster
                           
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                          • sireland67

                            sireland67 FABO Gold Member FABO Gold Member

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                            The car is a 73 Duster.

                            PxyPf0.jpg
                             
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                            • 72bluNblu

                              72bluNblu FABO Gold Member FABO Gold Member

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                              The 15x8" with 4.5" of backspace is generally the "magic formula" for a Duster/Demon that has an A-body 8 3/4 that's been converted to BBP axles. With the stock SBP axles 275/60/15's need more like 4.25" backspace. But with the body tolerances on these cars it's always a good idea to measure your own car from the wheel mounting surface back to the springs and out to the quarter lip. It's not unusual to have an axle offset slightly to one side or the other, or the body tolerances to be more than a 1/4" different from one car to the next or even from one side to the other.

                              Looks to me like a thin spacer will fix the issue, your car is high enough in the back that the quarter clearance shouldn't be a big issue. If you can get to 3/8" or so clearance on the springs you should be ok. Always better to have a little too much backspace than not enough, a 1/4" spacer is no big deal at all as long as you have enough threads on the wheel studs and it's a lot easier to install a spacer than move the quarter lip.

                              There are literally DOZENS of Dusters/Demons/Dart Sports running 275/60/15's on 15x8's on this board without issue. As I already mentioned the body tolerances on these cars were not super accurate, so it may be that your car can't run tires that size without modifications. But based on my own '74 Duster and many I've seen on this board it's much more likely that 275's will fit without "problems" if the backspacing is done correctly.

                              I had 275/40/17's on my '74 Duster with decent clearance for the street, and I'm currently running 295/35/18's with a 1/2" spring offset and some quarter lip trimming. 275's are tight, but they will fit most Dusters/Demons/Dart Sports as long as you account for the differences in width of the different axles and bolt patterns available for those cars.
                               
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                              • TF360

                                TF360 Well-Known Member

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                                Again, when you tell the average guy that 275's will fit, and they end up like the guy who started this thread. There is a problem. It can be very problematic (stressful) to order tires and rims, and then they don't fit after spending a lot of money. When recommending that size, we should always mention that there is probably a 50% shot they could end up like the OP. How many threads have we seen this same problem now? 255's are a better choice unless you are sure you have the space and/or your willing to modify something
                                 
                              • 72bluNblu

                                72bluNblu FABO Gold Member FABO Gold Member

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                                There are far more Dusters/Demons/Dart Sports with 275's mounted on them successfully than cars that they didn't work on. The OP's car will most likely be just fine with a 1/4 spacer and nothing else.

                                I'm well aware of problems in ordering rims, I've maxed out the rim and tire widths on pretty much all of my cars. And when I did it there were very few people running the sizes I run with the axle I have, so it was a lot of measuring, math and straight up guess work. I run 275/35/18's on the FRONT of my Duster and 295/35/18's on the back.

                                We've done this dance before, you can check all the threads. I'm not going to argue that 275's will fit your car, but I'm happy to provide all kinds of examples of them fitting just fine. I know there are more, but I have better things to do than look up every single example. There are plenty more.

                                Here's a dozen cars. Literally a dozen. Demon Rear Wheels I know you've seen it before because it was in response to you, but you can follow the link for the pictures or expand the quote for the links to each and every car.
                                Here's a thread with more
                                275/60/15 tires on stock Duster

                                Another one
                                Duster 275/60/15

                                You keep disagreeing and more and more members keep running 275's. Measured correctly they will work on the vast majority of Demons/Dusters/Dart Sports. And regardless, you should ALWAYS measure your own car because the body tolerances on these cars are fairly loose. The ballpark is about the same, but when you're maxing out the wheel well a 1/4" can make or break the fit. And you do have to account for the different width axles, because a SBP A-body 8 3/4 is not the same width as a BBP converted A-body 8 3/4. 7.25" and 8.25" rear axles are different from 8 3/4's too. So you can't just copy one person's backspacing, you have to match the whole combination.
                                 
                                Last edited: Sep 18, 2020
                              • xguard

                                xguard Member

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                                I measured incorrectly somewhere. I plan to find exactly where I messed up. For now I just want to get it going with minimal modifications.
                                 
                              • Slantsix64

                                Slantsix64 Well-Known Member

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                                I actually believe 275 60 15 looks better on a 7 inch rim fits better too
                                 
                              • 72bluNblu

                                72bluNblu FABO Gold Member FABO Gold Member

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                                The tire manufacturers disagree about it fitting better at least, both BFG and Cooper list a 7.5” as the narrowest rim a 275/60/15 should be mounted on.

                                That said, I’m sure plenty of people have run them on 15x7’s. The problem will be that if the tire is squeezed on a narrower rim the tread pattern will be distorted, so you’ll have to run a lower pressure to keep all the tread on the ground. Otherwise it kinda defeats the purpose of running the wider tire.
                                 
                              • 71GSSDemon

                                71GSSDemon Well-Known Member

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                                As a side note. The identical Wheel Vintique 15x8 with 4" bs and 275 60r15 were installed on my Dads 1969 Barracuda notchback. They also fit perfectly. He does have Mancini HD springs.
                                 
                              • AJ/FormS

                                AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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                                Move the springs; you won't regret it; I have fit 325/50-15s, on 10s, into the tubs of my 68 Barracuda, which is lowered. Yeah, I had to massage the inner metal a bit, but I did not roll the lips, just bent them up in one spot on each side.

                                I'm pretty sure the Barracudas and Duster/Demons share the same inner tubs.
                                 
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